Cylindrical type bellows are usually made either by a rolling process, or by radial expansion forming of successive corrugations. In the rolling process the entire tube being formed is rotated between shaped rolls to form each corrugation, the operation being slow and the apparatus cumbersome.
Expansion type machines have used a variety of mechanisms to form corrugations by stretching the tube outwardly with segmented mandrel elements. The tube is often inadequately supported due to the configuration and action of the mandrel, and distortion can occur. In some machines the mandrel does not form a complete ring when expanded and it may be necessary to rotate the tube to more than one position to form satisfactory corrugations.